docs: add multi-language output guide

Document how to configure OpenSpec to generate artifacts in languages
other than English using the existing context field in config.yaml.

Includes examples for Portuguese, Spanish, Chinese, Japanese, French,
and German, plus tips for handling technical terminology.

docs/multi-language-output.md

@@ -0,0 +1,217 @@
+# Multi-Language Output Guide
+
+Configure OpenSpec to generate artifacts in languages other than English.
+
+## Overview
+
+OpenSpec can output proposals, specs, designs, and tasks in any language by adding language instructions to your project's `context` configuration. This approach uses the existing config system without requiring any code changes.
+
+## Quick Setup
+
+### If you already have a config file
+
+Add a language instruction to your existing `openspec/config.yaml`:
+
+```yaml
+schema: spec-driven
+
+context: |
+  Language: Portuguese (pt-BR)
+  All artifacts must be written in Brazilian Portuguese.
+  Use Portuguese technical terminology where appropriate.
+
+  # Your other project context below...
+  Tech stack: TypeScript, React, Node.js
+```
+
+That's it. All generated artifacts will now be in Portuguese.
+
+### If you don't have a config file yet
+
+You can create one interactively or manually:
+
+**Option 1: Interactive setup**
+
+```bash
+openspec artifact-experimental-setup
+```
+
+This will guide you through creating `openspec/config.yaml` with schema selection, context, and rules.
+
+**Option 2: Manual creation**
+
+Create the file `openspec/config.yaml` in your project root:
+
+```bash
+mkdir -p openspec
+cat > openspec/config.yaml << 'EOF'
+schema: spec-driven
+
+context: |
+  Language: Portuguese (pt-BR)
+  All artifacts must be written in Brazilian Portuguese.
+EOF
+```
+
+## Language Examples
+
+### Portuguese (Brazil)
+
+```yaml
+context: |
+  Language: Portuguese (pt-BR)
+  All artifacts (proposals, specs, designs, tasks) must be written in Brazilian Portuguese.
+  Use Brazilian Portuguese conventions for technical terminology.
+```
+
+### Spanish
+
+```yaml
+context: |
+  Idioma: Español
+  Todos los artefactos deben escribirse en español.
+  Utilizar terminología técnica en español cuando sea posible.
+```
+
+### Chinese (Simplified)
+
+```yaml
+context: |
+  语言：中文（简体）
+  所有产出物（提案、规格、设计、任务）必须用简体中文撰写。
+  技术术语可以保留英文原文，但说明应使用中文。
+```
+
+### Japanese
+
+```yaml
+context: |
+  言語：日本語
+  すべての成果物は日本語で作成してください。
+  技術用語は必要に応じて英語を併記可能です。
+```
+
+### French
+
+```yaml
+context: |
+  Langue : Français
+  Tous les artefacts doivent être rédigés en français.
+  Utiliser la terminologie technique française lorsque possible.
+```
+
+### German
+
+```yaml
+context: |
+  Sprache: Deutsch
+  Alle Artefakte müssen auf Deutsch verfasst werden.
+  Technische Fachbegriffe können auf Englisch beibehalten werden.
+```
+
+## How It Works
+
+The `context` field in `openspec/config.yaml` is injected into every artifact's instructions as an XML block:
+
+```xml
+<context>
+Language: Portuguese (pt-BR)
+All artifacts must be written in Brazilian Portuguese.
+...
+</context>
+
+<template>
+[Schema's template content]
+</template>
+```
+
+The AI assistant sees this context when generating any artifact and follows the language instruction.
+
+## Tips
+
+### Be Explicit About Scope
+
+Specify which parts should be in the target language:
+
+```yaml
+context: |
+  Language: Spanish
+  Write all prose, descriptions, and explanations in Spanish.
+  Code comments may remain in English for consistency with the codebase.
+  Variable names and code identifiers should stay in English.
+```
+
+### Handle Technical Terms
+
+Decide how to handle technical terminology:
+
+```yaml
+context: |
+  Language: Japanese
+  Write in Japanese, but:
+  - Keep technical terms like "API", "REST", "GraphQL" in English
+  - Provide Japanese explanations in parentheses for complex terms on first use
+  - Code examples and file paths remain in English
+```
+
+### Combine with Other Context
+
+Language settings work alongside your other project context:
+
+```yaml
+schema: spec-driven
+
+context: |
+  Language: Portuguese (pt-BR)
+  All artifacts must be written in Brazilian Portuguese.
+
+  Tech stack: TypeScript, React 18, Node.js 20
+  Database: PostgreSQL with Prisma ORM
+  Testing: Vitest + React Testing Library
+
+  Conventions:
+  - Use functional components with hooks
+  - Follow existing patterns in src/components/
+```
+
+## Verification
+
+To verify your language config is working:
+
+```bash
+# Create a test change
+openspec new change test-language
+
+# Check the instructions - should show your language context
+openspec instructions proposal --change test-language
+
+# Output will include:
+# <context>
+# Language: Portuguese (pt-BR)
+# All artifacts must be written in Brazilian Portuguese.
+# ...
+# </context>
+```
+
+## Limitations
+
+- Language instructions apply to **all** artifacts. You cannot set different languages for different artifact types.
+- The effectiveness depends on the AI model's proficiency in the target language.
+- Technical diagrams, code samples, and file paths typically remain in English regardless of language setting.
+
+## Future Considerations
+
+We're considering adding a dedicated `language` field to the config schema in a future release:
+
+```yaml
+# Potential future syntax (not yet implemented)
+schema: spec-driven
+language: pt-BR
+```
+
+For now, the `context` approach described above is the recommended method. It provides full flexibility and works with all current versions of OpenSpec.
+
+## Related Documentation
+
+- [Project Config Demo](./project-config-demo.md) - Overview of project configuration
+- [Experimental Workflow Guide](./experimental-workflow.md) - Full workflow documentation